Single-base mutations and small deletions in chromosomal DNA result in the activation of oncogenes, inactivation of tumor suppressor genes, and the malfunction of other genes involved in cancer development and progression. These genetic changes are used in the new discipline of Molecular Medicine to screen individuals for predisposition to cancer, to diagnose and stage cancers, and to develop effective treatments. We will use Atomic Force Microscopy (AFM) to detect single-base mutations and small deletions in cancer genes. The as says we will develop are based on the detection of these mutations in heteroduplexes between the wild-type gene and patient DNAs. We will use specific nucleases to introduce single- or double- strand cuts in the hybrids at the site of mutations. The DNA products will be complexed with proteins which binds to the ends of single- and double-stranded nucleic acids and visualized with AFM. We will optimize our assays to detect mutations and will determine the sensitivity and specificity of our conditions. Our AFM assay will be useful in rapidly screening large patient samples with a minimum of cost in terms of reagents, sample preparation, and handling. PROPOSED COMMERCIAL APPLICATION: The AFM assay that we will develop will be used in diagnostic assays to detect mutations in human genes involved in cancer development and progression.